Mauna Loa geochemistry from 1843 to the 2022 eruption
摘要
In late 2022, Mauna Loa erupted for ~ 13 days from Moku‘āweoweo summit and the Northeast Rift Zone, the first eruption in nearly 38 years following decades of unrest. This study presents high-precision trace element concentrations and Pb-Hf–Nd-Sr isotopic compositions of 15 lavas that span the entire duration and spatial extent of the eruption. Subtle but consistent variations in the major, minor, and trace element concentrations and isotopic compositions of lavas with time that correlate with variations in seismicity suggest that magmatic processes such as shallow assimilation, magma mixing, and/or transport path control both seismicity and lava chemistry. These trends are used to identify the dominant process during each phase of the eruption whether shallow (assimilation of previous intrusions or solidified lavas with the establishment of the eruption) or deeper (pulses in magma transport from the shallow magma reservoir during the last 3 days of the eruption). The temperature of Mauna Loa lavas has fallen approximately 56 °C over the last 179 years, a time during which trace elements, MgO-normalized major elements, and isotopic compositions have co-varied. These geochemical trends suggest that the depths and degree of melting, as well as the amount of clinopyroxene and composition of a lithologically heterogeneous mantle source have changed with time. The increase in 87Sr/86Sr and 208Pb*/206Pb* with decreasing 143Nd/144Nd (i.e., increasingly isotopically enriched compositions) over the last ~ 60 years is likely related to the low magma flux during this time, which, taken along with increases in depth of melting and decrease in temperature, suggests that Mauna Loa may be entering its transition to the postshield volcanic stage.